The need for shielding electronic equipment both to prevent radiation of radio frequency energy from the equipment or to shield the equipment from external radiation is well known. While fully enclosing the circuit in a tight metal box would fully shield the circuit, this presents heat dissipation problems. Ventilated metal enclosures have heretofore been employed in which the air passes through a metal screen or through a metal honeycomb structure. While the honeycomb structure provides higher attenuation of radio frequency energy, these filters are expensive to manufacture and the tubular openings of the honeycomb structure tend to plug with dirt, reducing air flow and requiring a heavier duty fan than otherwise would be required.